Field of Invention
The present invention relates to a technical field of wireless communication, and more particularly to a method for measuring a time delay of a cluster system.
Description of Related Arts
In a wireless communication system, due to changes of terminal positions, a time point when a terminal signal reaches a base station is not able to keep pace with an air interface. As a result, a terminal signal strength which is actually received by a system and a success rate of demodulation are lowered. If a time delay is too large, inter-symbol interference will be caused and thus undermining an orthogonality of a multi-carrier, leading to a sharp decline in performance.
In order to solve a terminal time delay problem, a base station in a public network system measures a time delay of a terminal signal (mainly through SRS/RS) and timely notifies a terminal for providing TA adjustment, so as to ensure the terminal signal and an air interface are synchronized as far as possible when the terminal signal arrives at the base station. In a cluster system, due to limitations of group call service features resource constraints, the cluster system is not able to provide timely TA adjusting orders to group membranes.
For example, Chinese patent application, CN 201010241160.7,discloses a method for measuring a relative time delay in a wideband OFDM system, wherein during measurement of the relative time delay of a transmitting channel, different transmitting channels are distinguished by transmitting different sub-carriers of a frequency-domain sequence, and a frequency-domain of the transmitting channel, which satisfies a corresponding time-domain sequence, is defined as a cycle sequence. Therefore, when the transmitting channel transmits a time-domain sequence, only cycle data thereof is transmitted, so as to occupy a system time as little as possible. The frequency-domain sequence corresponding to an entire time-domain cycle sequence is determined by receiving the cycle data transmitted by different transmitting channels, and phase differences of non-null sub-carriers corresponding to each of the transmitting channels in the frequency-domain sequence are used for calculating the relatively time delay according to a proportional relationship between the relative time delay and phases, thereby improving a relative time delay measurement accuracy. That is to say, different transmitting channels are distinguished by transmitting different sub-carriers of the frequency-domain sequence, and the cycle sequence of the transmitting channel is defined; then the relatively time delay is calculated according to the proportional relationship between the relative time delay and the phases, thereby improving the relative time delay measurement accuracy. However, although the application is able to improve the accuracy to some extent, only self-estimated air interface time delay based on a downlink signal of the base station is considered for a phase time delay compensation, which is not combined with the terminal. Furthermore, achieving processes are complicated, and are only suitable for base station side processing.